[MRCA] RT-1439 PTT Input circuit?

[W2HX]

This is part of research to interface an HF radio with an RT-1439 (PRC-119) radio for purposes of cross band retransmit experiment.  If anyone is interested, I compared the RXMT keyline outputs of two candidate HF radios I have, the harris RF-5020 and the PRC-138 (RF-5200).  Someone brought to my attention that some care might be exercised when the PRC-138 pulls the keyline low to key another radio (in this case the RT-1439).  The output circuit of the PRC-138 may not be able to sink much current which is why I am inquiring about the PTT input to the 1439.

If anyone is interested, here are the two output circuits of the two radios.  The RF-5020 output looks more robust, I believe the inverter is really a darlington arrangement.  But since the PRC-138 might be a good solution for me, I am still cautious about that output circuit (74HC125 buffer).

http://www.w2hx.com/x/RXMTProject/

 
73 Eugene W2HX
 
From: milpack at yahoogroups.com [mailto:milpack at yahoogroups.com] On Behalf Of W2HX
Sent: Friday, August 31, 2012 11:59 AM
To: milpack at yahoogroups.com
Subject: [milpack] RT-1439 PTT Input circuit?

  
Hi all, anyone have a TM that shows how the PTT input line from the front audio connector interfaces to the rest of the radio? Meaning, what is on the other end of PIN C on the audio connector? Is it a TTL load? Is it a relay? Etc.

Thanks

73 Eugene W2HX